As shown in Patent Document 1, this kind of latching relay is arranged in such a way that DC forward and reverse currents are alternately caused to flow through an exciting coil of an electromagnet, and both ends of a movable iron piece alternately contact with the magnetic pole surface of each end of a fixed iron core, thereby causing the movable iron piece to make a reversal movement, and causing the reversal movement of the movable iron piece to switch electrical contacts. Further, the latching relay is arranged in such a way that a condition in which the movable iron piece is attracted to the magnetic pole surface of the fixed iron core is maintained by the magnetic force of the permanent magnet when the energization of the exciting coil is stopped to non-excite the electromagnet, thereby retaining a switched state of the electrical contacts.
This kind of heretofore known latching relay 100 comprises an electromagnet portion 110, a movable iron piece portion 120, a movable contact portion 130, a fixed contact portion 140, and the like, as shown in FIG. 19. The individual portions are assembled in advance into blocks, and disposed on a base member 102 formed from an insulating resin. Also, the movable iron piece portion 120 and movable contact portion 130 are linked via a sliding member 150. These members, after being disposed on the base member 102, are covered with a cover member.
The electromagnet portion 110 comprises a substantially U-shaped fixed iron core 111, a coil bobbin 112 insert molded integrally with the fixed iron core 111, an exciting coil 113 wound around the coil bobbin 112, and the like, as shown simplified in FIGS. 20(A), 20(B). Both ends of the exciting coil 113 are connected to a coil terminal 114. Also, an auxiliary yoke 122 bridged between magnetic pole pieces 111a and 111b formed of two respective legs of the fixed iron core 111 of the electromagnet portion 110 is provided between the magnetic pole pieces 111a and 111b. 
Also, the movable iron piece portion 120 comprises a substantially rectangular parallelepiped permanent magnet 121, an auxiliary yoke 122 to which the permanent magnet 121 is fixed, a movable iron piece 124 pivotally supported on the permanent magnet 121 via a pivotal support mechanism 123 (refer to FIG. 19), and the like, as shown simplified in FIGS. 20(A), 20(B).
The movable iron piece 124 is a substantially rectangular plate-like body formed by pressing, for example, a soft magnetic iron plate, and has a fulcrum protruding portion 124a formed in a substantially central portion of a surface facing the permanent magnet 121 so as to protrude to the permanent magnet 121 side (refer to FIGS. 20(A), 20(B)).
The permanent magnet 121 is disposed so that, for example, the auxiliary yoke 122 side is the N-pole, and the movable iron piece 124 side is the S-pole. When the movable iron piece portion 120 is assembled, the permanent magnet 121 is disposed so as to be sandwiched between the auxiliary yoke 122 and movable iron piece 124. As shown by the dashed arrows in FIG. 20(A), a magnetic flux emitted from the N-pole of the permanent magnet 121 passes through the auxiliary yoke 122, the magnetic pole piece 111a of the fixed iron core 111 attracting one end of the movable iron piece 124 with the excitation of the exciting coil 113, the movable iron piece 124, and the fulcrum protrusion 124a, and returns to the S-pole of the permanent magnet 121.
A condition in which the movable iron piece 124 is magnetically attracted by the fixed iron core 111 is maintained by this kind of magnetic action caused by the magnetic flux of the permanent magnet 121 even after the energization of the exciting coil 113 is stopped to switch the electromagnet 110 to a non-excited state.
The movable contact portion 130 is comprises a movable terminal 131 formed by bending a metal plate in a predetermined shape, a movable contact spring 132 formed of a spring sheet metal, a metal movable contact 133 fixed to the spring 132, and the like. Furthermore, a protruding portion 132a engaged with the sliding member 150 is formed at the leading end of the movable contact spring 132. Also, the fixed contact portion 140 is formed by bending a spring sheet metal in a predetermined shape, and configured of a fixed terminal plate 142 having a fixed terminal 141, a metal fixed contact 143, and the like.
A switching operation of the electrical contacts in this kind of latching relay 100 is as follows.
The condition of FIG. 19 is a condition in which the electrical contacts are in an off state. In this condition, as the upper end side of the movable iron piece 124 is magnetically attracted to the upper side magnetic pole piece 111a of the fixed iron core 111 by the magnetic flux of the permanent magnet 121 passing as shown by the dashed arrows in FIG. 20(A), the movable contact spring 132 is pulled to the electromagnet portion 110 side by the movable iron piece 124 via the sliding member 150, and the movable contact 133 separates from the fixed contact 143, meaning that the electrical contacts switch to the off state.
Herein, when an exciting current of a polarity which generates a downward magnetic flux is passed through the exciting coil 113, as shown by the solid arrow in FIG. 20(A), a magnetic attraction force is generated between the lower end portion of the movable iron piece 124 and the lower side magnetic pole piece 111b of the fixed iron core 111, and a magnetic repulsion force is generated between the upper end portion of the movable iron piece 124 and the upper side magnetic pole piece 111a of the fixed iron core 111, which contact with each other, meaning that the movable iron piece 124 pivots clockwise with the fulcrum protrusion portion 124a as its pivot fulcrum, and switches to the kind of condition shown in FIG. 20(B). As a result of this, the sliding member 150 linked to a protruding piece 124c of the upper end of the movable iron piece 124 is pushed in the direction of the movable contact spring 132. By so doing, the movable contact spring 132 linked to the other end of the sliding member 150 moves toward the fixed terminal plate 142, and the movable contact 133 fixed to the movable contact spring 132 contacts with the fixed contact 143 of the fixed terminal plate 142, thus switching the contacts to the on state.
As no more magnetic flux is formed by the electromagnet when the exciting current of the coil 113 is stopped, the magnetic attraction force of the lower side magnetic pole piece 111b of the fixed iron core 111 on the movable iron piece 121 becomes weaker. However, as a magnetic flux generated by the permanent magnet 121 passes through a closed magnetic path from the N-pole of the permanent magnet 121 through the auxiliary yoke 122 and movable iron piece 124 back to the S-pole of the permanent magnet 121, as shown by the dashed arrows in FIG. 20(B), the attraction of the lower end portion of the movable iron piece 124 to the lower side magnetic pole piece 111b of the fixed iron core 111 is maintained by the magnetic force caused by the magnetic flux, and the on state of the electrical contacts is retained.
In this condition, when the electromagnet is excited by causing a current of a direction opposite the heretofore described direction to flow through the exciting coil 113 so that an upward magnetic flux is generated, as shown by the solid arrow in FIG. 20(B), the upper side magnetic pole piece 111a of the fixed iron core 111 takes on a magnetic polarity which attracts the upper end portion of the movable iron piece 124, while the lower side magnetic pole piece 111b takes on a magnetic polarity which repulses the movable iron piece 124, and the upper end of the movable iron piece 124 is attracted to the upper side magnetic pole piece 111a. By so doing, the movable iron piece 124 pivots in a counterclockwise direction with the fulcrum protruding portion 124a as its pivotal fulcrum, and switches to the condition shown in FIG. 17(A). As a result of this, the sliding member 150 linked to the protruding piece 124c of the movable iron piece 124 moves in a direction away from the movable contact spring 132, thus causing the movable contact spring 132 linked to the other end of the sliding member 150 to move away from the fixed terminal plate 142. By so doing, the movable contact 133 of the movable contact spring 132 separate from the fixed contact 143 of the fixed terminal plate 142, and the electrical contacts switch to the off state.
As no magnetic flux is generated by the electromagnet when the exciting current of the exciting coil 113 is stopped, the magnetic attraction force of the upper side magnetic pole piece 111a on the movable iron piece 124 becomes weaker, but the magnetic force of the permanent magnet 121 acts, meaning that a condition in which the upper end portion of the movable iron piece 124 is in abutment with the upper side magnetic pole piece 111a of the fixed iron core 111 is maintained, thus retaining the electrical contacts in the off state.
In this way, with the latching relay 100, it is possible to switch the switching condition of the electrical contacts by switching the polarity of the exciting current passed through the exciting coil 113 of the electromagnet portion 110, and it is possible to retain a switched state of the electrical contacts with the permanent magnet even when the exciting current is stopped.